The present invention relates to a method and an apparatus for controlling the power of a transmit amplifier; in particular, a transmit amplifier in a mobile radio terminal.
FIG. 2 shows an outline circuit diagram of a conventional arrangement for controlling the power of a transmit amplifier PA. The signals sig which are supplied to the transmit amplifier PA to be amplified are amplified on the basis of a control parameter reg, which is supplied to the transmit amplifier PA and represents a measure of the gain or the gain factor, and are supplied to a directional coupler RK. The directional coupler RK outputs a small proportion of the power supplied from the transmit amplifier PA to the antenna ANT, and supplies this to a radio-frequency detector HFD, which converts this power to a DC voltage. This DC voltage value produced in this way is supplied as the actual value act to a comparison device V, where it is compared with a nominal value NOM which is preset by a control device, such as a microcontroller for a mobile radio terminal. The result of the comparison is output as a control parameter reg which adjusts the gain of the transmit amplifier PA such that the actual value corresponds to the nominal value nom. For this purpose, the gain factor is raised or lowered depending on the difference between the nominal value and the actual value. The majority of the power is supplied from the directional coupler RK to the antenna ANT, from where this power is transmitted in the form of radio-frequency signals.
EP-0388894 discloses the reception, at the receiving end, of a portion of the power which is transmitted from an antenna of a mobile radio terminal at the transmission end. This results in the disadvantage that the power control process includes a base station and, thus, the network infrastructure. This leads to slow control with inertia as well as to additional signaling complexity between the base station and the network infrastructure. As a result, this can be used only in mobile radio terminals which are operated in a mobile radio system which supports this type of power control.
Every effort is being made throughout the world to develop mobile radio terminals which are as small and light as possible. The use of a directional coupler is not consistent with this aim, since it is relatively large, heavy and complex to produce.
The present invention is, thus, directed toward a method and an apparatus for controlling the power of a transmit amplifier which allow the power to be controlled both easily and reliably, and, in particular, without using a directional coupler.